Knowing when to quit is a skill anybody can develop.
As far as start-ups are concerned, founders need to know when to give up because time is precious.
Seth Godin on Giving up vs Quitting
One software company I used to depend on has sort of given up. They have plenty of cash in the bank, but they simply stopped trying. You can feel it in their updates, their customer service, their approach to the future.
Giving up is a waste.
Quitting, on the other hand, is a fine thing to do. Because quitting gives you tomorrow back. It opens the door for the next contribution you are able to make.
In or out.
The top of the fence is no place to hang out.